Chemical Bond-is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
Most atoms are at relatively high potential energy. Atoms are less stable by themselves than combined with other atoms. By bonding with other atoms it decrease the potential energy, thus makes it more stable. Types of Chemical Bonding
Atoms’ valence electrons are redistributed when they bond, in order to make it more stable. Main-group metals lose electrons to form cations, and nonmetals gain electrons to form anions. Ionic bonding is a chemical bonding that result from the electrical attraction between cations and anions. In ionic bonding, atoms completely give up electrons to other atoms in order to be stabilized. Another chemical bonding is covalent bonding. Covalent bondingresults from the sharing of electron pairs between two atoms. In covalent bond, electrons are shared by atoms.
By calculating the differences in the elements’ electronegativities, we can determine the bonding of atoms. Nonpolar-covalent bondis a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge. Nonpolar-covalent bond’s electronegativity differences are between 0 and 0.3. Bonding that have electrons attracted by the ore-electronegative atom are polar. Polarmeans that they have an uneven distribution of charge. A polar-covalent bondis a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons. Their electronegativity differences fall from 0.3 to 0.7. Atoms in polar-covalent that are partial positive charged uses d+and partial negative chargedd–.
6-Section 2Covalent Bonding and Molecular Compounds
A moleculeis a neutral group of atoms that are held together by covalent bonds. A molecule of a chemical compound may consist of two or more atoms of the same element or two or more different atoms. Molecular compoundis a chemical compound whose simplest units are molecules. chemical formulaindicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. A molecular formulashows the types and numbers of atoms combined in a single molecule of molecular compound. A diatomic molecule is a molecule containing only two atoms. Formation of a Covalent Bond
Consider two atoms approaching each other. Each atom’s particles begin to interact. The nuclei and electrons are attracted to each other, thus decrease in the total potential energy of the atoms. But, the nuclei and electrons repel each other, and an increase in potential energy. The attractive force continues until a final distance is reached. Characteristics of the Covalent Bond: The distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms, is the bond length. Atoms release energy as they change from individual atoms to parts of a molecule. This same amount of energy must require separating the bonded atoms. Bond energyis the energy required to break a chemical bond and form neutral isolated atom. The Octet Rule:
Noble-gas atoms are very stable because their outer s and p orbitals are filled by a total of eight electrons. By sharing electrons with other, atoms can fill their outermost s and p orbitals through bonding. The bonding follows a certain rule, the octet rule, which states that; Chemical compounds tend to form so that teach atom, by gaining, or losing, or sharing electrons, has an octet of electrons in its highest occupied energy level. Electron-Dot Notationis an electron-configuration notation in which only the valence electrons of an atom of a particular element are show, indicated by dots placed around the element’s symbol. Lewis structuresare formulas in which atomic symbols represent nuclei and inner-shell electron pairs in covalent bonds, and dots adjacent to only on atomic symbol represent unshared electrons. A structural formula indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule. Single bondis a covalent bond in which one pair of electrons is shared between two atoms.
The Lewis structure of ozone is a resonance structure. Resonancerefers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure.
Lewis Structure:
1)Determine the total number of valence electrons
2)Determine the number of bonds each atom will form 3)Determine the central atom
- if you only have one of an element, it is almost always the central atom
-if Carbon is present, it is the central atom
4)Perpose a structure which allows for each atom to have its desired number of bonds. (COUNT ELECTRONS)
5)Distribute remaining electrons as lone pairs to satisfy octets. Count electrons again.
Example: H2O:
Step 1: Arrange the atoms: H O H
Step 2: Count up total valence electrons: 2(1) + 6 = 8 e- total
Step 3: Draw single bonds between central atom and surrounding atoms: H - O - H
Step 4: Place remaining electrons, in pairs, around appropriate atoms; start with outer atoms.
8 - 4 = 4 e- left; therefore 2 lone pairs to add:
-In this example, the 2 lone pairs must go around O, since H never gets lone pairsàH-O-H (lone pairs go on top and below the 'O'.)
Example 2:
Step 1: Arrange the atoms: B, Cl Cl, Cl
Step 2: Count up total valence electrons: 3(7) + 3 = 24 e- total
Step 3: Draw single bonds between central atom and surrounding atoms:
-->Cl
Cl B Cl
Step 4: Place remaining electrons, in pairs, around appropriate atoms; start with outer atoms.
24 − 6 = 18 e- left; therefore 9 lone pairs to add: (* means 3 surrounding lone pairs)
Step 5: Make sure all atoms that need octets have octets: The Cl’s have octets, so they’re okay; B is special element that can have an incomplete octet, so B only needs 6.
Step 5: Make sure all atoms that need octets have octets: done in Step 4
6-Section 3Ionic Bonding and Ionic Compounds
An ionic compoundis composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal.Formula unitis the simplest collection of atoms from which an ionic compound’s formula can be established. Formation of Ionic Compounds
In an ionic crystal, ions minimize their potential energy by combining in an orderly arrangement known as a crystal lattice. Crystal structures of compounds show how the atoms are arranged. Lattice energyis the energy released when one mole of an ionic crystalline compound is formed from gaseous ion.
6-Section 4Metallic Bonding
Due to the unique properties of metals, their chemical bonding is different than in ionic, molecular, or covalent compounds. Metallic Bondingis the chemical bonding that result from the attraction between metal atoms and the surrounding sea of electrons. Malleabilityis the ability of a substance to be hammered or beaten into thin sheets. Ductilityis the ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire. Dissolvebecomes part of a solution Dissociatesplitting of an ionic compound into its parts (cation and anion)
6-Section 5Molecular Geometry
VSEPR means “valence-shell, electron-pair repulsion”. VSEPR theorystates that repulsion between the states of valence-level electrons surrounding an atom caused these sets to be oriented as far apart as possible. In essence, the VSEPR theory states that electron pairs of electrons repel each other, therefore for a molecule to be at it’s most stable – electron pairs must be as far from each other as possible.
AB2 molecule is linear with 180 degree between each atom. AB3 molecule is called trigonal-planar, and each atom bears 120 degree angles. AB4 molecule is called tetrahedral, and the bond angles are 109.5 degree. Hybridization
Hybridization model is used to explain how the orbitals of an atom become rearranged when the atom forms covalent bonds. Hybridizationis the mixing of two or more atomic orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energies. Fore example, taking ethane, CH4. There are only 2 electrons in the 2p orbital, thus not filling in the entire orbital. We can then take 2s and 2p to combine the orbitals together, to create sp3. Hybrid orbitalsare orbitals of equal energy produced by the combination of two or more orbitals on the same atom.
Dipole: created by equal but opposite charges that are separated by a short distance.
Hydrogen bonding: the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule.
London Dispersion forces: the intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles.
· VSEPR theory is used to predict the shapes of molecules based on the fact that electron pairs strongly repel each other.
· Hybridization theory is used to predict the shapes of molecules based on the fact that orbitals within an atom can mix to form orbitals of equal energy.
· Intermolecular forces include dipole-dipole forces and London diepersion forces. Hydrogen bonding is a special case of dipole-dipole forces.
Practice Questions: True or False? if the underlined word is false, correct the answer.
1. A chemical bond results from the mutual attraction of the nuclei of atoms and electrons.
2. The electrons involves in the formation of a chemicals bond are called valence electrons.
3. As independent particles, atoms are at relatively low potential energy.
4. Atoms are more/less stable when they are combined.
5. The chemical bond formed when two atoms share electrons is called a covalent bond.
6. If the atoms that share electrons have an unequal attraction for the electrons, the bond is called ionic.
7. A molecule is a neutral group of atoms held together by covalent bonds.
8. Bond energy is the energy required to break a chemical bond.
9. The elements of the alkali metal group satisfy the octet rule without forming compounds.
10. Bonding in molecules or ions that cannot be correctly represented by a single Lewis structure is double bonding.
11. The chemical formula for an ionic compound represents the simplest ratio of the combined ions that balances total charges.
12. The ions in an ionic compound are organized into a crystal.
13. Compared with ionic compounds, molecular compounds have higher boiling points.
14. A polar molecule contains a region of positive charge and a region of negative charge.
15. The mixing of two or more atomic orbitals of similar on the same atom to produce new orbitals of equal energies is called dipole-dipole interaction.
Chemical Bond- is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
Most atoms are at relatively high potential energy. Atoms are less stable by themselves than combined with other atoms. By bonding with other atoms it decrease the potential energy, thus makes it more stable.
Types of Chemical Bonding
Atoms’ valence electrons are redistributed when they bond, in order to make it more stable. Main-group metals lose electrons to form cations, and nonmetals gain electrons to form anions.
Ionic bonding is a chemical bonding that result from the electrical attraction between cations and anions. In ionic bonding, atoms completely give up electrons to other atoms in order to be stabilized. Another chemical bonding is covalent bonding.
Covalent bonding results from the sharing of electron pairs between two atoms. In covalent bond, electrons are shared by atoms.
By calculating the differences in the elements’ electronegativities, we can determine the bonding of atoms.
Nonpolar-covalent bond is a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge. Nonpolar-covalent bond’s electronegativity differences are between 0 and 0.3. Bonding that have electrons attracted by the ore-electronegative atom are polar. Polar means that they have an uneven distribution of charge. A polar-covalent bond is a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons. Their electronegativity differences fall from 0.3 to 0.7. Atoms in polar-covalent that are partial positive charged uses d+and partial negative chargedd–.
6-Section 2 Covalent Bonding and Molecular Compounds
Formation of a Covalent Bond
Consider two atoms approaching each other. Each atom’s particles begin to interact. The nuclei and electrons are attracted to each other, thus decrease in the total potential energy of the atoms. But, the nuclei and electrons repel each other, and an increase in potential energy. The attractive force continues until a final distance is reached.
Characteristics of the Covalent Bond:
The distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms, is the bond length. Atoms release energy as they change from individual atoms to parts of a molecule. This same amount of energy must require separating the bonded atoms.
Bond energy is the energy required to break a chemical bond and form neutral isolated atom.
The Octet Rule:
Noble-gas atoms are very stable because their outer s and p orbitals are filled by a total of eight electrons. By sharing electrons with other, atoms can fill their outermost s and p orbitals through bonding. The bonding follows a certain rule, the octet rule, which states that; Chemical compounds tend to form so that teach atom, by gaining, or losing, or sharing electrons, has an octet of electrons in its highest occupied energy level.
Electron-Dot Notation is an electron-configuration notation in which only the valence electrons of an atom of a particular element are show, indicated by dots placed around the element’s symbol.
Lewis structures are formulas in which atomic symbols represent nuclei and inner-shell electron pairs in covalent bonds, and dots adjacent to only on atomic symbol represent unshared electrons. A structural formula indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule. Single bond is a covalent bond in which one pair of electrons is shared between two atoms.
The Lewis structure of ozone is a resonance structure. Resonance refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure.
Lewis Structure:
1)Determine the total number of valence electrons
2)Determine the number of bonds each atom will form 3)Determine the central atom
- if you only have one of an element, it is almost always the central atom
-if Carbon is present, it is the central atom
4)Perpose a structure which allows for each atom to have its desired number of bonds. (COUNT ELECTRONS)
5)Distribute remaining electrons as lone pairs to satisfy octets. Count electrons again.
Example: H2O:
Step 1: Arrange the atoms: H O H
Step 2: Count up total valence electrons: 2(1) + 6 = 8 e- total
Step 3: Draw single bonds between central atom and surrounding atoms: H - O - H
Step 4: Place remaining electrons, in pairs, around appropriate atoms; start with outer atoms.
8 - 4 = 4 e- left; therefore 2 lone pairs to add:
-In this example, the 2 lone pairs must go around O, since H never gets lone pairsàH-O-H (lone pairs go on top and below the 'O'.)
Example 2:
Step 1: Arrange the atoms: B, Cl Cl, Cl
Step 2: Count up total valence electrons: 3(7) + 3 = 24 e- total
Step 3: Draw single bonds between central atom and surrounding atoms:
-->Cl
Cl B Cl
Step 4: Place remaining electrons, in pairs, around appropriate atoms; start with outer atoms.
24 − 6 = 18 e- left; therefore 9 lone pairs to add: (* means 3 surrounding lone pairs)
Step 5: Make sure all atoms that need octets have octets: The Cl’s have octets, so they’re okay;
B is special element that can have an incomplete octet, so B only needs 6.
Step 5: Make sure all atoms that need octets have octets: done in Step 4
6-Section 3 Ionic Bonding and Ionic Compounds
An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. Formula unit is the simplest collection of atoms from which an ionic compound’s formula can be established.Formation of Ionic Compounds
In an ionic crystal, ions minimize their potential energy by combining in an orderly arrangement known as a crystal lattice. Crystal structures of compounds show how the atoms are arranged. Lattice energy is the energy released when one mole of an ionic crystalline compound is formed from gaseous ion.
6-Section 4 Metallic Bonding
Due to the unique properties of metals, their chemical bonding is different than in ionic, molecular, or covalent compounds.Metallic Bonding is the chemical bonding that result from the attraction between metal atoms and the surrounding sea of electrons.
Malleability is the ability of a substance to be hammered or beaten into thin sheets.
Ductility is the ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire.
Dissolve becomes part of a solution
Dissociate splitting of an ionic compound into its parts (cation and anion)
6-Section 5 Molecular Geometry
VSEPR means “valence-shell, electron-pair repulsion”. VSEPR theory states that repulsion between the states of valence-level electrons surrounding an atom caused these sets to be oriented as far apart as possible.In essence, the VSEPR theory states that electron pairs of electrons repel each other, therefore for a molecule to be at it’s most stable – electron pairs must be as far from each other as possible.
AB2 molecule is linear with 180 degree between each atom. AB3 molecule is called trigonal-planar, and each atom bears 120 degree angles. AB4 molecule is called tetrahedral, and the bond angles are 109.5 degree.
Hybridization
Hybridization model is used to explain how the orbitals of an atom become rearranged when the atom forms covalent bonds. Hybridization is the mixing of two or more atomic orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energies. Fore example, taking ethane, CH4. There are only 2 electrons in the 2p orbital, thus not filling in the entire orbital. We can then take 2s and 2p to combine the orbitals together, to create sp3. Hybrid orbitals are orbitals of equal energy produced by the combination of two or more orbitals on the same atom.
Dipole: created by equal but opposite charges that are separated by a short distance.
Hydrogen bonding: the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule.
London Dispersion forces: the intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles.
· VSEPR theory is used to predict the shapes of molecules based on the fact that electron pairs strongly repel each other.
· Hybridization theory is used to predict the shapes of molecules based on the fact that orbitals within an atom can mix to form orbitals of equal energy.
· Intermolecular forces include dipole-dipole forces and London diepersion forces. Hydrogen bonding is a special case of dipole-dipole forces.
Practice Questions:
True or False? if the underlined word is false, correct the answer.
1. A chemical bond results from the mutual attraction of the nuclei of atoms and electrons.
2. The electrons involves in the formation of a chemicals bond are called valence electrons.
3. As independent particles, atoms are at relatively low potential energy.
4. Atoms are more/less stable when they are combined.
5. The chemical bond formed when two atoms share electrons is called a covalent bond.
6. If the atoms that share electrons have an unequal attraction for the electrons, the bond is called ionic.
7. A molecule is a neutral group of atoms held together by covalent bonds.
8. Bond energy is the energy required to break a chemical bond.
9. The elements of the alkali metal group satisfy the octet rule without forming compounds.
10. Bonding in molecules or ions that cannot be correctly represented by a single Lewis structure is double bonding.
11. The chemical formula for an ionic compound represents the simplest ratio of the combined ions that balances total charges.
12. The ions in an ionic compound are organized into a crystal.
13. Compared with ionic compounds, molecular compounds have higher boiling points.
14. A polar molecule contains a region of positive charge and a region of negative charge.
15. The mixing of two or more atomic orbitals of similar on the same atom to produce new orbitals of equal energies is called dipole-dipole interaction.
Answers: 1) True 2) True 3) False, High 4) More 5) True 6) False, Polar 7) True 8) True 9) False, Noble Gas 10) False, Resonance 11) True 12) True 13) Flase, Lower
14) True 15) False, Hybridazation
Sources: Davis, Raymond E., Mickey Sarquis, Regina Frey, and Jerry L. Sarquis. Modern Chemistry. Austin, Texas: Holt, Rinehart and Winstron, 2006. ii-949, http://tinyurl.com/mma4x8, http://www.scottsdalecc.edu/chemistry/docs/lewdstps.pdf, http://tinyurl.com/mp95bq